Yale team claims forward-osmosis success

A forward-osmosis technology described as “engineered osmosis” has been developed in the USA by a Yale University spinoff company called Oasys.

Professor Menachem Elimelech and graduate students Robert McGinnis and Jeffrey McCutcheon claim that their device reduces the energy needed to purify water to one-tenth of that required by conventional desalination systems.

Unlike conventional reverse-osmosis systems, forward osmosis establishes an osmotic pressure gradient instead of using pressure or heat to force water through a semipermeable membrane. A highly concentrated “draw” solution is used to induce a net flow of water through the membrane into the draw solution, thus effectively separating the feed water from its solutes.

The biggest challenge, according to Aaron Mandell, CEO of Oasys, was identifying a concentrated solution that could be removed efficiently and entirely. Details of Oasys’s draw solution are a company secret, but it uses ammonia and carbon-dioxide gases dissolved in water in specific proportions.

The solution can be reused after being removed from clean water, and the membrane required is also nearly identical to those already used in reverse osmosis. While other companies are doing forward osmosis, Oasys claims that its draw solution makes its technology much more efficient.

Oasys estimates that engineered osmosis will cost US$ 0.37-0.44/m³ once fully scaled up. The startup has so far established a pilot-scale plant to test the technology by producing 1 m³/d.

Mandell says that Oasys is raising venture financing that will be put toward scaling to around 1,000-10,000 m³/d, still well below the scale of many commercial desalination plants.